This invention relates to a decoding device for decoding a device input signal read out of a recording medium on which an encoded signal is recorded.
The encoded signal is produced by an encoding device which is for interframe predictive encoding a digital video signal. The digital video signal is, for example, a television signal and comprises successive frames or pictures of a common frame period. The interframe predictive encoding is effective to encode the digital video signal into an encoded signal having a low bit rate. The interframe predictive encoding makes use of a correlation factor between adjacent ones of the pictures or frames. In the interframe predictive encoding, a difference is encoded between corresponding picture elements of two successive pictures to provide the encoded signal. The interframe predictive encoding is generally used in transmitting the digital video signal. The interframe predictive encoding is also used in a video signal processing system which is for use of the recording medium, such as a compact disk read-only memory (CD-ROM), in record and/or reproduce the digital video signal.
In this connection, it is preferable that the compact disk read-only memory can be operable like a video tape in performing not only a normal or forward reproduction but also a reverse or backward reproduction. More specifically, the digital video signal has a zeroth or leading frame to an end or trailing frame which are processed into leading through trailing compressed video signals, respectively, when the digital video signal is subjected to the interframe predictive encoding. The digital video signal is successively recorded on the recording medium from the leading compressed video signal to the trailing compressed video signal in a normal or forward order. Merely for convenience of description, the zeroth through the end frames may be understood to correspond to zeroth through end scenes, respectively. On carrying out the reverse reproduction, the digital video signal is reproduced from the end scene in a reversed or backward order in response to a request issued by an operator or user to indicate the reverse reproduction.
Such a video signal processing system is disclosed in a prior U.S. patent application Ser. No. 189,249 which was filed May 2, 1988, by Toshio Koga, Junichi Ohki, Mutsumi Ohta, and Hideto Kunihiro for assignment to the present assignee and c/o NEC Home Electronics, Ltd. The above-named Mutsumi Ohta is the instant applicant. The Ohta et al patent application corresponds to a prior Canadian patent application No. 565,485 which was filed Apr. 29, 1988, and was filed on the basis of Japanese patent application No. 108352/1987 and others. In the prior patent applications, the video signal processing system is called an image processing system. The digital video signal is called a sequence of image signals.
The prior patent application does not make use of a filter for removing quantization noise which is generated and remains in either an encoding loop of an interframe predictive encoding device or a decoding loop of an interframe predictive decoding device. It is known in the art that the quantization noise is generated and remains in either the encoding loop or the decoding loop. Generation of the quantization noise results in a reduction of the quality of pictures reproduced by each of the normal and the reverse reproductions.
Another video signal processing system is disclosed in another prior United States patent application which was filed May 30, 1989, under the title of "Method of coding a digital video signal for reverse reproduction of pictures", by Mutsumi Ohta for assignment to the present assignee. The above-named Mutsumi Ohta is the instant applicant. The Ohta patent application corresponds to another prior Canadian patent application which was filed May 30, 1989, and is based on Japanese patent application No. 133477/1988. The latter prior patent application does neither use a filter for removing quantization noise which is generated in either the encoding loop or the decoding loop.